The present invention relates to a bioabsorbable composition for bioabsorbable articles such as sutures, clips, staples, pins, screws, tacks, sponges, gauzes, implants or prostheses suitable for introduction into a living body. More particularly, the present invention is directed to a bioabsorbable composition associated such as by filling or coating, with a bioabsorbable article so as to protect the article from premature hydrolytic degradation upon storage and/or to facilitate delivery of the article and associated therapeutic agents to a wound site.
This invention provides a method for improving the storage stability of polymeric articles having an inherent tendency to undergo degradation when exposed to water or a humid atmosphere, probably as a result of hydrolysis. More particularly, the invention is directed to improving the storage stability of articles and devices such as absorbable surgical sutures, clips, staples, implants, protheses and the like, fabricated from polymers which are susceptible to hydrolytic degradation, notably, polymers and copolymers of glycolic acid (i.e., hydroxyacetic acid), the cyclic dimer of glycolic acid ("glycolide"), lactic acid, the cyclic dimer of lactic acid ("lactide") and related monomers.
Polymers and copolymers of the foregoing kind and absorbable surgical devices made therefrom are well known. See, e.g., U.S. Pat. Nos. 2,668,162; 2,703,316; 2,758,987; 3,225,766; 3,297,033; 3,422,181; 3,531,561; 3,565,869; 3,620,218; 3,626,948; 3,636,956; 3,736,646; 3,772,420; 3,773,919; 3,792,010; 3,797,499; 3,839,297; 3,867,190; 3,878,284; 3,982,543; 4,060,089; 4,137,921; 4,157,437; 4,234,775; 4,237,920; 4,300,565; and, 4,523,591; U.K. Patent No. 779,291; D K Gilding et al., "Biodegradable polymers for use in surgery--polyglycolic/poly(lactic acid) homo- and co-polymers: 1, polymer, volume 20, pages 1459-1464 (1979), and D. F. Williams (ed.), Biocompatibility of Clinical Implant Materials, Vol. II, ch. 9: "Biodegradable Polymers" (1981). The biodegradability of these polymers/copolymers is believed to be due to the hydrolytic attack of their ester linkages by aqueous body fluids although the exact mechanism involved has been a matter of speculation.
An absorbable device (e.g., an absorbable suture or other aqueous body fluid-absorbable article) may experience prolonged storage before use, e.g., periods of several months and sometimes even several years. In order to prevent water or humidity in the storage environment from contacting the article and compromising its in vivo strength to the point where the article is no longer serviceable, it is common practice to package the article in an essentially moisture impermeable enclosure. However as noted in U.S. Pat. Nos. 3,728,839 and 4,135,622, any package material which prevents the entry of moisture will also prevent the escape of moisture. Thus, any moisture associated with or absorbed by the article at the time it is packaged will tend to remain in the package for the entire period of its storage.
According to aforesaid U.S. Pat. Nos. 3,728,839 and 4,135,622, the in-vivo strength of polyglycolic acid surgical elements such as sutures undergoes significant deterioration on long term standing in the package, even on exposure of the contents to very small amounts of water for very short periods of time, e.g., 20 minutes or less, just prior to packaging due to the aforenoted tendency of a moisture impervious package to seal the moisture in with the suture.
To prevent hydrolytic degradation of the suture or to minimize its extent, U.S. Pat. Nos. 3,728,839 and 4,135,622 disclose removing moisture from the suture before sealing the package so that virtually no water remains in the package once the package is sealed. This approach to improving the suture's storage stability, while effective, is in practice difficult and expensive to carry out. Prior to sealing the suture within its moisture impervious package, it is essential that the suture be "bone dry", a condition achieved by heating the suture for a sufficient period to remove the water therefrom, e.g., 180.degree.-188.degree. for 1 hour under a 26 inch vacuum. However, once the water is removed, the suture cannot be allowed to contact a moisture-containing environment even for a limited duration since as previously noted, even brief exposure to moisture can cause severe deterioration of suture in vivo strength. It therefore becomes necessary following the water removal step to temporarily store the suture in a dry area, i.e., an environment which is essentially free of moisture, where the possibility of contact with moisture is largely eliminated.
Considered in their entirety, these operations for improving the storage stability of absorbable sutures and other surgical devices which are susceptible to hydrolytic degradation amount to a time consuming, expensive and relatively complex solution to the storage stability problem.
In addition, although coating braided sutures has long been known and practiced, see, e.g., U.S. Pat. No. 3,297,033, prior to the present invention it has been difficult to coat solid bioabsorbable articles, notably fairly rigid articles such as clips, tacks, staples, because the coatings often tend to flake or peel off the coated article. This is especially a problem when the article is being implanted in a living body, e.g., by firing from instruments. Provision of an adherent bioabsorbable coating upon surgical articles is especially desirable because certain additives can be incorporated into the coating, such as various growth factors, which could not withstand processing conditions for forming the bioabsorbable articles themselves.